Electron Spin Resonance Studies on Melanin

Blois, Marsden S.; Zahlan, A. B.; Maling, J.E.

doi:10.1016/s0006-3495(64)86797-7

Cited by 209 publications

(144 citation statements)

References 11 publications

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“…The calculated g values for the signal from nonlabeled green spores were 2.00407 (with diphenylpicrylhydrazyl as a standard) and 2.00415 (with Bruker strong pitch as a standard). These two values are within the range of the g (4,9,45). The shape of the signal corresponds to that described for melanins-it was slightly asymmetric without hyperfine structure.…”

Section: Vol 6 2007 Cytoplasmic Parameters In Fungal Spores 163supporting

confidence: 81%

High Viscosity and Anisotropy Characterize the Cytoplasm of Fungal Dormant Stress-Resistant Spores

Dijksterhuis

Nijsse²,

Hoekstra³

et al. 2007

Eukaryot Cell

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Ascospores of the fungus Talaromyces macrosporus are dormant and extremely stress resistant, whereas fungal conidia-the main airborne vehicles of distribution-are not. Here, physical parameters of the cytoplasm of these types of spores were compared. Cytoplasmic viscosity and level of anisotropy as judged by spin probe studies (electron spin resonance) were extremely high in dormant ascospores and during early germination and decreased only partly after trehalose degradation and glucose efflux. Upon prosilition (ejection of the spore), these parameters fell sharply to values characteristic of vegetative cells. These changes occurred without major volume changes that suggest dramatic changes in cytoplasmic organization. Azide reversibly inhibited prosilition as well as the decline in cytoplasmic parameters. No organelle structures were observed in etched, cryoplaned specimens of ascospores by low-temperature scanning electron microscopy (LTSEM), confirming the high cytoplasmic viscosity. However, cell structures became visible upon prosilition, indicating reduced viscosity. The viscosity of fresh conidia of different Penicillium species was lower, namely, 3.5 to 4.8 cP, than that of ascospores, near 15 cP. In addition the level of anisotropic motion was markedly lower in these cells (h 0 /h ؉1 ‫؍‬ 1.16 versus 1.4). This was confirmed by LTSEM images showing cell structures. The decline of cytoplasmic viscosity in conidia during germination was linked with a gradual increase in cell volume. These data show that mechanisms of cytoplasm conservation during germination differ markedly between ascospores and conidia.Ascospores of the fungus Talaromyces macrosporus are sexual structures that exhibit extreme resistance to heat, high pressure, drought, and freezing (14, 15). They contain an extremely high level of trehalose (13) and have relatively low amounts of water in an aqueous environment. The spores show constitutive dormancy in rich media, and germination is triggered and synchronized by a short heat treatment at 85°C. Ascospores of T. macrosporus can germinate after 17 years of storage (40) and belong to the most resilient eucaryotic structures described hitherto. They can survive a heat treatment at 85°C for 100 min or high pressurization at 1,000 MPa for 5 min (14). Upon heat activation, the spores degrade their trehalose within 100 min, followed by a rapid release of glucose into the bathing medium up to 10% of the cell wet weight. After 2.5 h, the outer cell wall opens, and the protoplast encompassed by the inner cell wall is ejected in a fast process (seconds) termed prosilition. The ejected cell then swells and forms a germ tube, resembling events that occur in other fungal spores. Conner et al. (10) studied the cellular basis of heat resistance in relatively young (11-day) and older (25-day) ascospores of Neosartorya fischeri exhibiting different heat resistance levels (D 82 of approximately 23 and Ͼ60 min, respectively). The ascospores showed differences in the inner cell wall region at the lateral ridge...

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Section: Vol 6 2007 Cytoplasmic Parameters In Fungal Spores 163supporting

confidence: 81%

High Viscosity and Anisotropy Characterize the Cytoplasm of Fungal Dormant Stress-Resistant Spores

Dijksterhuis

Nijsse²,

Hoekstra³

et al. 2007

Eukaryot Cell

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“…Since the singlet signal has an organic origin, paramagnetism of the poly-semiquinone radical can be assumed to dominate the molecular structure of Sepia inks. 14) Although the g-values found were similar (ca. 2.00) across these samples, we found that the ESR line width decreased with increases in the size of the particles.…”

Section: Optical and Paramagnetic Properties Of Size-controlled Ink Pmentioning

confidence: 83%

Optical and Paramagnetic Properties of Size-Controlled Ink Particles Isolated fromSepia officinalis

Matsuura¹,

Hino²,

Akutagawa³

et al. 2009

Bioscience, Biotechnology, and Biochemistry

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“…In particular, this large body of work has shown that there are two populations of unpaired spins in melanin: "intrinsic" spins derived from carbon centered radicals remaining from the polymerisation process (8) and the "semiquinone" or "extrinsic" spin regulated by the comproportionation equilibrium (Scheme 1) (35). In solid-state samples, the intrinsic spin is predominantly observed (8,36), whereas the extrinsic spin is predominantly seen in melanin solutions or colloidal suspensions (35,37).…”

Section: Resultsmentioning

confidence: 99%

Role of semiconductivity and ion transport in the electrical conduction of melanin

Mostert

Powell

Pratt

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

335

452

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Melanins are pigmentary macromolecules found throughout the biosphere that, in the 1970s, were discovered to conduct electricity and display bistable switching. Since then, it has been widely believed that melanins are naturally occurring amorphous organic semiconductors. Here, we report electrical conductivity, muon spin relaxation, and electron paramagnetic resonance measurements of melanin as the environmental humidity is varied. We show that hydration of melanin shifts the comproportionation equilibrium so as to dope electrons and protons into the system. This equilibrium defines the relative proportions of hydroxyquinone, semiquinone, and quinone species in the macromolecule. As such, the mechanism explains why melanin at neutral pH only conducts when "wet" and suggests that both carriers play a role in the conductivity. Understanding that melanin is an electronic-ionic hybrid conductor rather than an amorphous organic semiconductor opens exciting possibilities for bioelectronic applications such as ion-toelectron transduction given its biocompatibility.bioelectronics | electrical properties | biomacromolecules | ionic conduction T he melanins are responsible for multiple critical functions in humans such as photoprotection and free radical scavenging (1). These molecules are also found in the substantia nigra of the human brain stem where their exact biological role is unknown; however, it has been speculated that neuromelanin may be involved in neural transmission (2). Melanin phototoxicity is also implicated in deadly melanoma skin cancer (3, 4). Despite decades of intense studies across biology, chemistry, and physics, the full details of the structure and functions of the melanins are still not clearly understood. Eumelanin, the major component in human skin pigment is viewed as the archetypal "true" melanin (here we adopt the standard nomenclature in which the terms "eumelanin" and "melanin" are used interchangeably). Eumelanin is composed of aggregated oligomeric and polymeric species based upon the indolic monomers 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and their various redox forms (1). These monomers are randomly cross-linked to form planar sheets, stacked via aromatic π-interactions and with varying conjugation length and character (5, 6, 7). For many years, melanins were considered as extended linear homo-or heteropolymers with a conjugated backbone (8). However, this view no longer has any credence and the disordered 2D protomolecular sheet model is now widely accepted. This sheet model has quite profound implications for the treatment of melanins within a conventional polymer framework, and many of the standard methods and theories for probing structure property relationships in macromolecules are inadequate or simply do not apply.Two properties of melanin have particularly intrigued physicists and chemists for decades: (i) Melanins are electrical conductors showing photoconductivity in the solid state; and (ii) melanins are black with broad featureless opt...

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Electron Spin Resonance Studies on Melanin

Cited by 209 publications

References 11 publications

High Viscosity and Anisotropy Characterize the Cytoplasm of Fungal Dormant Stress-Resistant Spores

High Viscosity and Anisotropy Characterize the Cytoplasm of Fungal Dormant Stress-Resistant Spores

Optical and Paramagnetic Properties of Size-Controlled Ink Particles Isolated fromSepia officinalis

Role of semiconductivity and ion transport in the electrical conduction of melanin

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